Week 5: Making Manganese Ligands

This week I tried more reactions for making some manganese ligands, most of which did not work. Last week I was able to make manganese oxalate by combining ammonium bicarbonate and oxalic acid and then adding manganese acetate. This procedure did not work for the other ligands I tested, although I am hoping to try it next week with formic acid and pyruvic acid. I also added potassium permanganate to benzoic, citric, and ascorbic acids, but this method was not productive either, although I tried several variations of the procedure. We did further testing of the manganese oxalate method from last week, including measuring the stability of the complex over time. When the ligand exchange first takes place to make manganese oxalate from manganese acetate and ammonium oxalate, the solution is a bright pink color, but that color quickly decreases with time, as does the reactivity. In order to have reproducible and comparable results later, it is important to know how fast this color change occurs, since it is not possible to always have exactly the same amount of time between making and measuring a solution. Matt taught me how to use a different spectrophotometer than the plate reader I normally use, and we used the computer to which it is connected to take snapshots of the spectrum over time. This essentially means that we were able to watch the color of the solution change from pink to almost clear over the course of a few hours. I plotted the absorbance values versus time, and I will use that graph to correct for any delays in measurements I make in the future. For the manganese ligands I have successfully made, in I worked on fine-tuning my testing procedures to get more precise kinetic data.